1. Field of the Invention
The present invention relates in general to a body comprising a steel member serving as a base body and a ceramic member soldered thereto, and more particularly to the bodies of a type which is particularly used as an engine component, such as rocker arm, intake valve, exhaust valve, valve lifter, piston, turbo-charger rotor or the like.
2. Descritpion of the Prior Art
In order to clarify the task of the present invention, the description will be commenced with respect to a conventional metal type rocker arm used in an internal combustion engine.
For production of the rocker arm, a steel such as S40C steel (Japanese Industrial Standard) is forged to provide a base body. The base body is thermally treated to achieve homogenization thereof. Then, the body is machined to form a contact portion. A wear tip of metal is welded to the contact portion by means of high frequency welding. Thereafter, the body is finely machined to have required shape and dimension.
However, it has been revealed that usage of the metal wear tip shortens the life of the rocker arm because of the poor durability of the metal tip against wearing.
In view of this drawback, several measures have been hitherto proposed, one being disclosed in Japanese Utility Model First Provisional Publication No. 59-91404, and the other being disclosed in Japanese Patent First Provisional Publication No. 61-191572. That is, in the former case, a wear tip made of a ceramic is soldered to a metal rocker arm body with a certain buffer member interposed therebetween. The buffer member is used to relax the thermal expansion difference between the ceramic tip and the metal rocker arm body. In the latter case, a martensite type stainless steel is used as the rocker arm body. In this case, the hardening of the body is secondarily achieved by the heat applied when the wear tip is welded to the rocker arm body.
However, these two measures still have the following drawbacks. That is, in the former case, the heat applied for welding the ceramic tip to the rocker arm body tends to anneal the metal rocker arm body to an impracticable degree. Furthermore, in the latter case, the production cost of the rocker arm is increased considerably because of usage of the martensite type stainless steel which is expensive.